At present, the usual termination devices are generally square and have outwardly directed deflecting surfaces extending along their sides outwardly of the mouth of the combustion air intake pipe to protect against the effects of strong winds. It has been found, however, that there is a serious problem with the present termination devices when there are winds having a velocity in the range of 5 to 15 kilometers per hour. In such circumstances, the flame becomes unstable and eventually goes out because the air intake becomes reversed and the air required to support combustion in the firebox is lacking.
This lack of combustion air appears to be a result of the hot exhaust fumes heating air in the intake duct causing an outward air flow aided by any venturi effect or reduction of atmospheric pressure due to vortexes and wakes in the intake region at the mouth of the intake duct reversing air intake at these low velocity winds.